1. Field of the Invention
The present invention relates to a storage management system, and in particular to a technology for controlling data reallocation between or among memory areas which are controlled by the storage management system.
2. Description of the Related Art
A storage management system comprises and constructed by at least one storage apparatus which is referred to as, for example, a disc array sub-system. This storage apparatus has drives such as hard disc drives and semiconductor memory drives located and constructed in an array form, and provides a memory area which is based on RAID (Redundant Array of Independent Disks). A host computer (hereinafter referred to as “host”) accesses to a logical memory area provided by the storage apparatus to read/write data.
The amount of data managed in organizations such as corporations, local governments, educational institutions, financial institutions, government and other public offices, by the way, is continuing to expand year by year, and the amount of data increases, storage apparatuses are added and replaced. In order to handle such increased amount of data and complicated system configuration, it is proposed to improve utility efficiency of storage apparatuses by reallocating data handled by an application program such as a mail management software and a database management software, to an appropriate position in accordance with how frequently the data is accessed, and the like. See Japanese Patent Application Laid-Open (Kokai) No. 2001-67187 (FIGS. 4-6).
Also in Japanese Patent Application Laid-Open (Kokai) No 2003-140836 (FIGS. 3-4), a method is proposed in which after all disc apparatuses in the system are classified from performance point of view and the order of performance among classes is defied in advance, data in a memory area of a high rate of use by the disc apparatus is reallocated to a class of a higher-performance. In the document, a data reallocation control technology is disclosed in which a sufficient unused area for reallocation is ensured by reallocating data from the high-performance class to a low-performance class before performing the reallocation to the high-performance class, in case no unused area was found in the high-performance class selected as a reallocation destination.
In each of the above-mentioned patent documents, a technology is disclosed in which data stored in one volume is copied to another volume based on information on performance and usage of disc to reallocate the data.
However, the technology as described in JP 2001-67187 is not convenient for use because it requires reallocating data individually by each volume unit, and does not allow a volume to be moved between or among classes which are freely defined by the user. In the technology as described in JP 2003-140836, when a sufficient empty area is not left in the class selected as a reallocation destination, an empty area is obtained by unconditionally reallocating an area of low rate of usage by the disc apparatus, out of the areas classified as the class, to a class of lower performance (in the following description, not only reallocation to a lower-performance class but also reallocation for obtaining a sufficient empty area for reallocation will be referred to as “expelling data”). Since the user of data has been unable to specify the way in which an expelling target and an expelling destination class are selected, there is a possibility that a class selected as an expelling destination for the data selected as the expelling target does not correspond to the data reallocation destination which the user of the data originally assumed.